I have an idea for building a rear storage box on the back of my 1987 Toy Itasca ... I know the bumper really isn't built to hold a lot of weight, so I was thinking of building a box that attaches directly to the outside rear wall of the coach ... I would like it just to hold my generator (about 40 pounds), a 5 gallon can of gas and my spare tire. Anybody ever do anything like that? Am I crazy, stupid, naive ... ? All of the above?